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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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HIDDEN, FOURTH AM) SMALLER GLACIERS
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as revealed by soundings, are considered in Chapter XI. Careful observations showed that the delta advanced 1600 feet between 1899 and 1910, and, as stated on an earlier page, 900 or 1000 feet of this advance came between 1905 and 1909, the increased rate in delta growth during the later period doubtless being due to the large amount of alluvial material supplied during the two mile advance. This rapid rate of growth, 145 to 225 feet a year, is remarkable, for the much larger Mississippi delta advances only 262 feet a year, the Danube 800 to 400 feet, and the Tigris-Euphrates seventy feet annually, though small glacier streams are normally much more heavily loaded with sediment than the rivers mentioned. Seal Bay is 180 to 600 feet deep.. This part of Russell Fiord shoreline was probably not uplifted during the 1899 earthquakes, so the 1600 foot advance cannot be ascribed to a change of level of the land. The 1600 foot advance of the Hidden Glacier delta is shown in a spectacular way in Plate LXXXII, where the upper photograph shows the Harriman Expedition vessel, the George W. Elder, anchored in June, 1899, at a point shown to be dry land in the lower photograph taken in June, 1910.
Recession 1910 to 1913. In September, 1913, the junior author made more detailed observations of Hidden Glacier than on any other Yakutat Bay glacier visited by the International Geological Congress. The recession of the front of the glacier by melting was estimated to be 400 to 500 feet. The imperfect fosse which existed in 1909 and 1910 was destroyed. The outwash plain in front of the glacier was graded at a lower and flatter level than in 1910, but fragments of the older alluvial fans existed as isolated flattish-topped hills. An abandoned marginal gorge, cut 40 to 60 feet in the older gravels of the north valley wall, no longer had a stream. There were pits in front of the glacier, showing by slumping that buried ice existed on the site of the glacier terminus of 1909-10. Icebergs of small size were floating down the larger glacial streams to the sea. At the northern margin the Hidden Glacier had thinned at least 150 feet vertically and shrunk several hundred yards from the push moraine of the advance of 1907. The crevasses of the glacier surface were largely subdued by ablation. Isolated lateral ice remnants rested on the overridden gravels.
TABULAR STATEMENT OP KNOWN CHANGES IN HIDDEN GLACIER
Year	Nature and amount of change	Recorded by
Up to 1891	Probably retreat	Russell
1891-1895	Probably continued retreat	Boundary Survey
1895-1899	Retreat about 500 feet	Gilbert
1899-1905	Retreat about 1300 feet	Tarr and Martin
1905-1906	Continued slight retreat	Tarr
1906-1909	Advance over 10,000 feet; slight retreat	Tarr and Martin
1909-1910	Slight retreat	Martin
1910-1913	Retreat, 400-500 feet; thinning 150 feet	Martin